Abstract
The ocular effects of substance P (SP) were studied in 13 normal volunteers. Various concentrations of SP (0.135, 1.35 and 135 μg per 100 μl) were instilled into the conjuctival sac and pupillary area changes were evaluated by means of an electronic pupillometer. The ability of SP to modify the mydriasis induced by pretreatment with 1% homatropine eyedrops was also studied. The instillation of SP produced miosis in a dose-dependent manner without provoking any ocular disturbances. Furthermore, the highest concentration tested was unable to reduce the homatropine-induced mydriasis. These findings indicate that SP exerts a pupillokinetic action in humans which probably occurs via a receptor mechanism. Since muscarinic blockade is not overcome by the peptide instillation, the results do not clarify whether SP causes miosis acting on iris muscles and/or cholinergic fibres.
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